Underwater laser cladding in full wet surroundings for fabrication of nickel aluminum bronze coatings

Underwater laser repairing technology as a new type of on-line maintenance technology will promote the development of oceanographic engineering. However, there are many difficulties during the process of underwater laser repairing. In this paper, underwater laser cladding process in full wet surroundings (or WULC, for short) for fabrication of nickel aluminum bronze (or NAB, for short) has been reported, and laser cladding process in the air for fabricating NAB coatings was used for comparative study. The homemade protective covering was used to solve the problems of underwater laser repairing. For comprehending the effect of full wet surroundings and protective covering on microstructure and electrochemical performance of the NAB coatings, a series of characterization tests including SEM, EDS, XRD and TEM and a series of electrochemical measurements were carried out. The alloy coatings fabricated by WULC possess good formability through optimizing the processing parameters. The elements distribution of the coatings shows different patterns compared to conventional cast copper alloy and NAB coating fabricated by laser cladding in the air. In addition, the ordered solid solution and twinning structure have been observed in the WULC-NAB coatings. These unique microstructures and elements distribution patterns caused the better electrochemical performance of NAB coating fabricated by WULC. These findings suggest that the idea of using a protective layer in underwater laser cladding in full wet surroundings is feasible. The WULC process reported in this paper can provide some theoretical guidance for repairing damaged parts in full wet surroundings.